These days, coatings are produced, among other things, using sputtering processes and arc processes, which are part of so-called PVD processes (PVD: physical vapor deposition). In this technique, targets are pulverized or vaporized. In these processes, the targets get hot and must be cooled.
According to the prior art, the cooling is carried out for example by means of a so-called cooling plate of the foil cooling plate type, which cools the back of the target, as shown in FIG. 2. The pressure of the cooling medium presses the foil against the target and thus achieves a good thermal conduction from the cooling medium to the target.
Depending on the power input, the heat dissipation via the cooling plate, and the thermal conductivity of the target material, the targets are heated differently and expand in accordance with their longitudinal expansion coefficients. The target in this case must be able to expand freely so that it is not destroyed.
For process-related reasons, it is important for the target resting on the cooling, plate to expand concentrically to the cooling plate axis so that during the entire operation, a concentric gap can be ensured between the target and the surrounding components or the surrounding component. In particular, it is very important for the target to expand in a centered fashion relative to the cooling plate axis in order to avoid short-circuits that can occur, for example, if the target is operated as a cathode and the target has an anode ring positioned around it, to which a different electrical potential is applied, as shown for example in FIG. 2.
If the target is not correctly centered, then the target does not expand concentrically enough. As a result, electrical short-circuiting can occur between the anode ring and the expanded target.
In the present example, the position of the target relative to the anode ring is determined by its position on the cooling plate. With a small gap between the cooling plate and target, the position of the target is sufficiently defined and no contact occurs between the target and anode. This small gap, however, strictly limits the possible expansion of the target. The maximum permissible target temperature or operating temperature is thus predetermined and the maximum sputtering power is thus limited. The smaller the gap, the lower the permissible sputtering power is.
With a larger gap, the target is as a rule positioned eccentrically on the cooling plate. In addition, the eccentric support causes the mechanical stresses in the target to be uneven during the operation of foil cooling plates. Depending on the target material, this can result in permissible mechanical stresses being exceeded.
The object of the present invention is to create a plate-holding device system that makes it possible to keep a plate centered in a holder device regardless of the temperature of the system; the plate is able to freely expand in the holder device so that it is not destroyed during the expansion process.